Capacitors suffer from aging, as you know. the problem is associated with the electrolyte "drying out" if not used for a few years, and then the capacitor(s) suffer from "shock" and then draw high current often with catastrophic results.So a possible solution is to use a variac to slowly increase the voltage . this helps the mains filter capacitor(s). For the secondary circuits an external current limiting power supply (or some current limiting inserted into the circuit) is needed to slowly increase the voltage on those circuits. This can take many hours to days.There are many articles to search for and read on "reforming capacitors". I have a variac if you need to borrow oneHope this helps

GrantChivers wrote:So a possible solution is to use a variac to slowly increase the voltage . this helps the mains filter capacitor(s).

Thanks Grant. I would consider a variac for a very old and rare computer I might want to restore but for relatively common ones like these I prefer the "turn 'em on and let 'em blow" technique. Those AC filter caps from computers of the early 80s are easy and cheap to replace.

In fact in a few of my computers (the TRS-80 Model 4 is one I can think of), I've replaced those old caps as a preventative measure. They always seem to blow.

Good on you Tezza for rescuing these machines. The platinums might not be particularly sought after by those with museums for houses lol but they are stillclassics in my book, just wish I lived nearer you now:-(